Researchers develop 'super' yeast that turns pine into ethanol

November 18, 2011

Researchers at the University of Georgia have developed a "super strain" of yeast that can efficiently ferment ethanol from pretreated pine -- one of the most common species of trees in Georgia and the U.S. Their research could help biofuels replace gasoline as a transportation fuel.

"Companies are interested in producing ethanol from woody biomass such as pine, but it is a notoriously difficult material for fermentations," said Joy Doran-Peterson, associate professor of microbiology in the Franklin College of Arts and Sciences.

"The big plus for softwoods, including pine, is that they have a lot of sugar that yeast can use," she said. "Yeast are currently used in ethanol production from corn or sugarcane, which are much easier materials for fermentation; our process increases the amount of ethanol that can be obtained from pine."

Before the pinewood is fermented with yeast, however, it is pre-treated with heat and chemicals, which help open the wood for enzymes to break the cellulose down into sugars. Once sugars are released, the yeast will convert them to ethanol, but compounds produced during pretreatment tend to kill even the hardiest industrial strains of yeast, making ethanol production difficult.

Doran-Peterson, along with doctoral candidate G. Matt Hawkins, used directed evolution and adaptation of Saccharomyces cerevisiae, a species of yeast used commonly in industry for production of corn ethanol, to generate the "super" yeast.

Their research, published online in Biotechnology for Biofuels, shows that the pine fermented with the new yeast can successfully withstand the toxic compounds and produce ethanol from higher concentrations of pretreated pine than previously published.

"Others before us had suggested that Saccharomyces could adapt to harsh conditions. But no one had published softwood fermentation studies in which the yeast were pushed as hard as we pushed them," said Doran-Peterson.

During a two-year period, Doran-Peterson and Hawkins grew the yeast in increasingly inhospitable environments. The end result was a strain of yeast capable of producing ethanol in fermentations of pretreated wood containing as much as 17.5 percent solid biomass. Previously, researchers were only able to produce ethanol in the presence of 5 to 8 percent solids. Studies at 12 percent solids showed a substantial decrease in ethanol production.

This is important, said Doran-Peterson, because the greater the percentage of solids in wood, the more ethanol that can be produced. However, a high percentage of solids also places stress on the yeast.

"Couple that stress with the increase in toxic compounds, and the fermentation usually does not proceed very well," she said.

Pine is an ideal substrate for biofuels not only because of its high sugar content, but also because of its sustainability. While pine plantations account for only 15 percent of Georgia's trees, they provide 50 percent of harvested timber, according to Dale Greene, professor of forest operations in UGA's Warnell School of Forestry and Natural Resources. The loblolly pine that Doran-Peterson and Hawkins used for their research is among the fastest growing trees in the American South.

"We're talking about using forestry residues, waste and unsalable timber," said Peterson, "Alternatively, pine forests are managed for timber and paper manufacturing, so there is an existing infrastructure to handle tree-farming, harvest and transportation for processing.

"The basic idea is that we're trying to get the yeast to make as much ethanol as it can, as fast as it can, while minimizing costs associated with cleaning or washing the pretreated pine. With our process, no additional clean-up steps are required before the pine is fermented," she said.

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""We're talking about using forestry residues, waste and unsalable timber," said Peterson, "Alternatively, pine forests are managed for timber and paper manufacturing, so there is an existing infrastructure to handle tree-farming, harvest and transportation for processing."

Assuming they stick to the first part of that (e.g., using waste) it would seem to be purely beneficial. However, the same forestry products industry mentioned is under great scrutiny due to over-forestation. This almost sounds like the beginning of the "grow corn for biofuel" idea that has turned into such an enormous boondoggle in the United States, and has partially resulted in higher food prices.

Paper manufacturing using the sulfite process produces significant amount of fermentable sugars as a by-product. Last time I heard they were used for making ethanol though must've been in the prohibition times.

Nowadays they just dry and burn the stuff to make steam for the mills, which also makes the process net positive in energy.

However, the same forestry products industry mentioned is under great scrutiny due to over-forestation. This almost sounds like the beginning of the "grow corn for biofuel" idea that has turned into such an enormous boondoggle in the United States, and has partially resulted in higher food prices.

Actually, as reported on physorg and elsewhere, the forestry industries in europe and america are now sustainable, and our forests are even increasing slightly - In virgin forests, they usually leave enough trees for the forest to recover quickly now. In other places, they replant. They also have large tree farms where they have special fast growing trees suited for paper or board use.

Of course, if this goes full tilt, it may change the equation, but currently there is plenty of waste wood that is burned.

Also, this research is good because methanol is highly toxic, so turning it into ethanol instead is good. Wood can provide more feedstock too.

Actually, as reported on physorg and elsewhere, the forestry industries in europe and america are now sustainable, and our forests are even increasing slightly - In virgin forests, they usually leave enough trees for the forest to recover quickly now.

Guess it depends on who you ask. From Wiki:

Since 1963 there has been a steady decrease of forest area with the exception of some gains from 1997. Gains in forest land have resulted from conversions from crop land and pastures at a higher rate than loss of forest to development. Because urban development is expected to continue, an estimated 93,000 square kilometres (23,000,000 acres) of forest land is projected be lost by 2050,[4] a 3% reduction from 1997. Other qualitative issues have been identified such as the continued loss of old-growth forest,[5] the increased fragmentation of forest lands, and the increased urbanization of forest land.[6]

My comments are regarding new research, but even the wikipedia entry points to a stable forest area. A loss of 3% over 53 years equates to an average loss of just .056% a year.

So if the numbers on wikipedia are off by less than a tenth of a percent a year, it can swing the other way.

My point is not to say the more recent research is necessarily correct and wikipedia is wrong - my point is that forest cover in america is indeed approximately stable. This is well supported from wikipedia - Where even they report a previous year of growth in 97.

Ethanol is a terrible fuel and developing technology and infrastructure around it is a huge mistake. But very profitable I suppose.

I agree that it's a mistake if ethanol is the primary goal of production. A fine example of this is corn harvests being converted to fuel. However, if the process is used to reduce waste material and produce a profit, I am all for it.

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